Do honest people know for certain when others are dishonest? Can dishonest people also detect when other dishonest people are lying?

No one honest. We all liers cus we all lied once. But I think if the man says the lie he knows when another says the truth, but honest one can't be sure that somebody lies or not cus he thinks that everyone says the truth as he does... Though everybody thinks that everyone another does the same what he does

Not always, innocent people get conned sometimes. Dishonest people also get duped sometimes.

Yes. There are certain tells. If you were observant, you would have seen "his honor" drinking a lot of water, nervous fidgeting, sticking his tongue in his cheek, hesitating on his answers, not looking people in the eye... all signs of lying. Well, that and the really, really bad acting too.